A stone is thrown upward from a bridge at a speed of 10 m/s. It narrowly misses the bridge on the way back down and hits the water at 30 m/s. The bridge is about
A) 3 m high.
B) 20 m high.
C) 50.5 m high.
D) 76.5 m high.

Question

Quizplus · Accepted Answer

The stone's speed increases by 10 m/s on the way down to the bridge level, and then by another 20 m/s to reach 30 m/s at the water. Using the equation $v^2 = u^2 + 2gh$, where $v = 30$ m/s, $u = 0$ m/s, and $g = 10$ m/s², we find $h = 45$ m. Adding the height from the bridge to the peak (5 m), the total height is 76.5 m.

A Stone Is Thrown Upward from a Bridge at a Speed